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Saturday, July 17, 2010

Hub Caps

The next job was to machine the polycarbonate hubcaps.

The first step was to cut out a somewhat circular shape on the bandsaw. Then I center drilled it and and put it in the lathe for pressure turning. Pressure turning is when you use a centering bit/cone and press the workpiece against the chuck:

Doing this allowed me to round the edge and get a precise diameter.

Note the scratches from the chuck teeth- I didn't have enough pressure on them.

The next step was to take it out of the lathe, change the chuck, and grasp the outer circumference so that I could bore out the bearing surface. It turns out that I needed to take off about 8 thousandths less than the bearing OD for a nice fit. That seems like a lot, but polycarb is significantly softer than metal.

The four outer hubcaps.

Next, I needed to do the inner side hubcaps. These required a 2in bearing surface hole all the way through. So the first thing I did was take a 1.75" hole saw to them:

The hole saw was a pain because of the massive amount of friction it made and the tiny amount of surface area I could clamp (all of them spun in the clamps at least once). Then I put them on the lathe and cleaned up the inner surface.

Next came mill work. I needed to bore 10 holes (5 for an alignment pin and 5 for 4-40 screws) and cut a 3/32" o-ring groove. EZ-Trak to the rescue:

Note the ultra-thin parallels.
It worked pretty well.


 All that's left for these is cutting the 1/16" polycarb endplates for the inner-side hubcaps and threading the 4-40 holes. 

All that's left to do for a test motor is: 
1. The above
2. laser cutting acrylic spacers and hall-effect board
3. winding a stator
4. cutting alignment pins
5. gluing magnets
6. assembling

Oh and: 

soldering lots of surface mount stuff on two S-Electronics 3PH Duo's. Oh boy.


  1. What was the difference between the two outer side caps that made one bearing pocket's axial face clean and the other kinda rough?

    (All mine are kinda rough...what's the secret to clean pockets?)

  2. you have way more patience than i do

  3. Hey nice work!

    I really recommend that you try molding your own wheels! It is really fun process!

    But a lot of work to create the molds. I did my own tracks for a 4inch pipe cleaning robot. It was fun!

    We used this stiff blue wax for the molds. It was CNC to perfection!

    I hope you luck and can't wait to see the final product!

    btw- I am sure 2WD will be plenty!